Slack adjuster



March 20, 1962 K. w. BROLING 3,025,932

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NNN Wm W NW NW fi5$$ m n %M figwfifi w W W m w mm NM\W Q mom w MI P w an m G ml N N In I ll I I Ill V Marh 20, 1962 K. w. BROLING SLACK ADJUSTER 8 Sheets-Sheet 2 Filed Feb. 19, 1959 I I l- M. h/Bralz'fj +1 WAI 4 WW March 20, 1962 K. w. BROLING SLACK ADJUSTER Filed Feb; 19, 1959 8 Sheets-Sheet 3 Jhue/zaar Kia'f WBrZzn 9 f 73AM? 777gW/M March 20, 1962 w, BROLING SLACK ADJUSTER 8 Sheets-Sheet 4 Filed Feb. 19, 1959 K. W. BROLING SLACK ADJUSTER March 20, 1962 8 Sheets-Sheet 5 Filed Feb. 19, 1959 8 Sheets-Sheet 6 K. W. BROLING SLACK ADJUSTER mwuxu kkw b ik Qk March 20, 1962 Filed Feb. 19, 1959 QQMN atom/W! March 20, 1962 K. w. BROLING SLACK ADJUSTER 8 Sheets-Sheet 7 Filed Feb. 19, 1959 March 20, 1962 K. w. BROLING SLACK ADJUSTER Fi led Feb. 19, 1959 8 Sheets-Sheet 8 United States Patent 3,025,932 SLACK ADJUSTER Keith W. Broling, Homewood, Ill., assignor to Universai Railway Devices Company, a corporation of Delaware Filed Feb. 19, 1959, Ser. No. 794,363 Claims. (Cl. 188-200) This invention relates to slack adjusters for the braking systems of railway cars, and it relates particularly to such slack adjusters that have a two-way adjusting action for either taking up or letting out slack in the braking system.

Two-way slack adjusters have been known for many years but have failed to gain any degree of acceptance because of operational and maintenance problems involved in the slack adjusters that have been proposed and used.

Thus, in the slack adjusters as heretofore proposed, the apparatus has been dependent upon various types of clutches that have been found to be unduly sensitive and hard to maintain in use. Such clutching arrangements have included friction clutches, and wedge-type clutches, and these clutching devices have been found to be unreliable in use. In another form of two-way slack adjuster that has been used reliance has been had on a rotative adjusting nut movable along a fairly long lead adjusting screw, and in such slack adjusters, the particular lead employed upon the screw threaded member has in most instances been such that the adjusted position of the device might be disturbed in the course of the sudden impacts that are often encountered in coupling and switching operations in a railway yard. Another difiiculty that has been found in prior two-way slack adjusters has been that the mechanism has been of such a character as to require substantially full enclosure so that where dirt did accumulate within the housing of such structure it could not be released therefrom in the courseof normal use. Hence the devices were not self cleaning as is required with equipment used in the braking system of railway cars.

In the view of the foregoing it is the primary object of the present invention to provide a two-way slack adjuster which overcomes the foregoing difficulties and objections so as to be reliable and effective in use. An object related to the foregoing is to provide such a twoway slack adjuster that will withstand the rough usage and which will maintain its adjusted position even though the equipment may be subjected to sudden impacts.

Another important object of the present invention is to provide a two-way slack adjuster that is extremely rugged in character and which does not require a full enclosure of the operating parts, thus to render the slack adjuster self cleaning to the extent that is required in railway brake apparatus. A related object is to provide a two-way slack adjuster in which the slack adjusting forces required in either take up or let out of the slack are minimized so as to avoid the necessity for utilizing any substantial portion of the brake applying forces in the operation of the slack adjusters.

As above pointed out, the slack adjuster of the present invention is of such a character as to withstand sudden impacts such as those encountered in coupling and switching operations without disturbing the adjustment of the device, and another important object of the present invention is to enable this to be accomplished by elements of the apparatus that are utilized in the adjustment of slack, and to enable the working forces of the brake applying operation to be taken by other means included in the slack adjuster so as to thereby protect the adjusting elements of apparatus from the relatively large forces that are involved in the brake application.

The present two-way slack adjuster is adapted particularly for association with the dead lever of a foundation braking system, and in the course of the normal operation of such a dead lever of a braking system, the lever has certain inherent movements that are induced by the fundamental characteristics of normal railway braking systems, and a further and important object of the present system is to enable these normal movements of the dead lever of a braking system to be utilized and coordinated with the slack adjusting system to minimize the forces required for attaining the two-way slack ad justing operation.

Other and further objects of the present invention will be apparent from the following description and claims, and are illustrated in the accompanying drawings, which,

by way of illustration, show a preferred embodiment of tures of the present invention and associated with the braking system;

FIG. 1A is a fragmentary portion of the system shown in FIG. 1 with the push rod and related parts in their released relationship;

FIG. 2 is a side elevational view of the apparatus shown in FIG. 1;

FIG. 3 is a side elevational view of the slack adjuster shown in FIG. 1;

FIG. 4 is a horizontal cross sectional view of the unitwise direction in order to conserve space, the view being taken from the line 55 of FIG. 4;

FIG. 6 is a vertical sectional view taken through the unitof FIG. 4 the view being taken along the line 6-6 of FIG. 4;

FIG. 7 is a bottom plan view of the portion of the unit, the view being taken from the line 7-7 of FIG. 3; FIG. 8 is a schematic timing diagram illustrating the push rod travel and the pull rod travel in a long stroke, a normal stroke, and a short stroke thereof, and further illustrating the movements of the rack of the unit in the related brake release cycles;

I FIGS. 9, 10 and 11 are. schematic views similar to FIG. 3 and showing the important operating parts of the slack adjusting unit in a normal length operating stroke; FIG. 9 representing the parts in their at rest positions; FIG. 10 representing the fully operated positions, and FIG. 11 representing the released or at rest positions at q the end of the cycle;

FIGS. 12 to 14 are views similar to FIGS. 9 to 11 a take up operation of the unit.

l trates the position of the parts at the end of the brake- FIGS. 15 and 16, considered along with FIG. 14, show the different positions of the parts in a normal operation that follows a take up operation so that FIG. 15 illus- Patented Mar. 20, 1.962

applying operation that follows a take up cycle, while FIG. 16 illustrates the parts after the release of the brakes;

FIGS. 17 to 22 are diagrammatic views that illustrate a short cycle of the apparatus as well as the next normal cycle; FIG. 17 illustrating the normal at rest position; FIG. 18 illustrating the end of a short stroke brake applying operation; FIG. 19 showing the parts when the unit has partially returned toward its at rest position and FIG. 20 showing the fully returned position of the parts after the performance of the let-out operation; and as to the next normal cycle, FIG. 21 shows the parts when the brakes are fully applied, while FIG. 22 shows the parts at the end of the brake release operation.

The Apparatus and Its Association With the Braking System For the purposes of disclosure the present invention is illustrated herein as embodied in an automatic two-way slack adjusting unit 20 and is shown as applied to the adjustment of the anchoring pivot of the dead lever 21 of a conventional foundation braking system for railway cars. The slack adjusting unit 20 is mounted on the car frame adjacent to the stationary pivot point of the dead lever 21 of the braking system so that the dead lever 21 may be operatively connected to the unit 20, as will be described, and each time the car brakes are operated through an application and release cycle the slack adjusting unit 20 is operated through a cycle in which the unit is responsive to push rod travel to maintain the same slack adjustment, to take up slack, or to let out slack, as determined by such push rod travel.

For operating the unit 20 in accordance with push rod travel, the unit 20 has a laterally extending rock shaft 22 connected thereto, as will be explained, and a lever 23 fixed to the shaft 22 has a pull rod 24 connected thereto and extending lengthwise of the car to a point adjacent and roughly parallel to the path of movement of the push rod 25 of a brake cylinder 26. The push rod 25 has a bracket 25B thereon which connects the push rod to one end of the live lever 21L, and the bracket 25B is extended laterally from the push rod 25 and the pull rod 24 extends through this bracket. The pull rod 24 has stop or abutment nuts 27 thereon that are so adjusted that after the push rod 25 has been advanced for a predetermined distance, the bracket 255 will engage the nuts 27 andwill impart rocking movement to the rock shaft 22 in accordance with the length of the stroke of the push rod 25. This rocking movement thus varies in accordance with Whether or not the braking system has slack therein within the normal or correct range, or embodies too much or too little slack, and in accordance with the extent of the rocking movement of the shaft 22, the auto matic slack adjusting unit 20 is effective when required to either take up or let out slack in the system, as will be described.

The Structure of the Unit 20 The unit 20 comprises an elongated U-shaped housing 30 that is fixed as by brackets 30B to an element of the car frame, and within the housing 30' an anchoring or traction means in the form of a relatively long slack adjusting rack R is mounted for longitudinal movement. The end of the dead lever 21 is connected by a brake lever pin 31 to the right hand end of the rack R as shown in FIGS. 1 and 4. t

At one side of the housing 30 and near the left hand end thereof as shown in FIG. 4, an exterior housing 32 is mounted which contains a rocking assembly 34 which has a projecting lug 35 for connecting the end of the rock shaft 22 to the assembly 34. The lug 35 i located at one side of a squared recess 34R formed in an axial relation in the assembly 34, and after the squared end of the shaft 22 is inserted into the socket or recess 34R, it is locked in position. by a pin extended through the shaft 22 and the lug 35. The rocking assembly 34 has a lever 36 projecting radially therefrom, and this lever, at its end, has a spring rod 38 pivoted thereto, the other end of the spring rod being slidable through a bracket 39 formed on the housing 3% and there being a spring 40 acting between the bracket 39 and an enlarged flange 38F formed on the rod 33. The spring rod 3 8 thus acts nor mally to urge the rocking assembly 34 in a clockwise direction to the position shown in FIG. 3, and this position is determined by a nut 39F which engages the bracket 39. When the brakes are applied and the pull rod 24 is pulled to the right, as shown in FIGS. 1 and 3, the rocking assembly 34 is rocked in counterclockwise direction, FIG. 3, through a rocking stroke which in extent represents the length of the stroke of the push rod 25. This stroke length therefore constitutes a mechan cal indica tion as to whether slack adjustment is proper or Whether slack needs to be taken up or let out, and means are associated therewith the rocking assembly 34 for accomplishing such automatic adjustment as required.

The rack R is somewhat T-shaped in cross section as will be evident in FIG. 6 of the drawings, and at its left end, as viewed in FIGS. 1 and 3, the rack R extends through an opening 42 formed in an end wall 43 of the housing 3%. An angle bar 44 is mounted on the wall 43 to provide an elongated surface alongwhich the rack R may slide, and a similar angle 45 is mounted on the end wall 43 at opening 42 to provide a similar relatively long contact surface for engaging the upper teeth of the rack to guide the same.

At its right hand end, the rack R has an enlarged head H which forms a bifurcation through which the brake lever pin 31 extends in connecting the dead lever 21 of the system to the rack R, it being noted that the dead lever 21 extends through an elongated slot 398 formed in the side Wall of the housing 36. The enlarged head H also is utilized in guiding and supporting the right hand end of the rack R. Thus, as shown in FIGS. 3 and 5, a pair of angle bars 46 are fixed on the inner sides of the housing 30 to support the head H in the longitudinal sliding movement of the rack R.

It is by longitudinal adjustment of the rack R that the slack in the braking system is adjusted, the rack R being shifted to the left in FIG. 3 to take up slack, and being shifted to the right in FIG. 3 to let out slack. This is accomplished by mechanism located in the housing 30 and actuated by the rocking assembly 34.

The rack R, as hereinabove pointed out, is generally T-shaped in cross section and has a series of rack teeth U cut into its upper surface, these teeth being flat-topped and relatively broad, but being at a predetermined spacing for purposes that will hereinafter appear. In the lower face of the rack, a series of rack teeth L are formed upwardly into the bottom surface, the teeth L having the same spacing as the teeth U, but being more nearly pointed in character and having their opposite faces at a somewhat greater slope.

The T-shaped form or" the rack R provides flanges F that are located along the bottom edges of the rack and these flanges are utilized as mounting and supporting means for other structural elements of the adjuster.

Thus, a take-up carriage 50 has a generally U-shaped formation, as will be evident in FIG. 6, and near its open upper face has a pair of inwardly facing grooves 51 that slidably embrace the two flanges P so that the carriage 50 may be supported on and beneath the rack R and may be reciprocated along the track R, as will be described. The carriage 50 has a take-up pawl 52 pivoted thereon between the opposite sides of the right hand end portion of the carriage 50 and the pivotal support is provided by transverse pin 53. The pawl 52 extends in the left hand direction from its pivot 53 as will be evidentin FIG. 3, and it has a forward end face that is disposed at such an angle that when the pawl is pivoted clockwise into a tooth space, the end face will be parallel to the face of the tooth that is located just to the left of such end face, and with this relationship the application of endwise pressure engaging these faces will act to hold the pawl 52 in its engaged relationship with respect to the tooth L with which it has been engaged.

The take-up pawl 52, however, tends to drop by gravity out of its engaged relationship, but at certain times in the cycle of operation of the mechanism, the pawl is yieldingly urged toward an engaged relationship with respect to the rack. In the present instance, this is accomplished by a pawl weight 55 that is pivoted on the pivot pin 53. The pawl weight 55 is extended to the right from the pivot pin 53 so as to normally tend to rock in a clockwise direction about the pin 53, and a pair of arms 55A extend to the left in spaced relation from the pawl weight 55 on opposite sides of the pawl 52 and to the left as viewed in FIG. 7, and these arms are connected by a follower pin 55? so that the pin 55F may engage the lower surface of the pawl 52 to urge the same yieldingly toward an engaging relation to the respective rack. As above pointed out, however, this yielding engaging force is applied to the pawl 52 in a controlled manner according to the position of the lower carriage 50. This involves a cam action in which a lateral extension of the pin 55P engages as a cam follower with a stationary cam 57. The cam 57 is triangular in its general form and has a face 57L on its left hand side as viewed in FIG. 3, and it has a face 57R on its right hand side, and these faces 57L and 57R diverge upwardly, as will be evident in FIG. 3. The cam 57 is located in a fixed position on the inner side of the left hand wall of the housing 30, as viewed in FIG. 6, so that the cam 57 is effective to disable the pawl weight 55 during certain portions of a reciprocating stroke of the carriage 50, as will be described.

Above the rack R, and generally above the location of the carriage 50, an upper or let-out carriage 66 is mounted, and this upper carriage is generally U-shaped in form so that the carriage 60 rides along the upper surface of the rack R and has downwardly projecting flanges 60F along the sides of the rack to locate the carriage 60 thereon. The carriage 60 is held against undesired upward displacement by close spacing of the top wall of the housing 30. The carriage 60 has a let-out pawl 62 pivoted thereon by a transverse pivoted pin 63, and the pawl 62 extends in a right hand direction from the pivot 63 and has a forward or end face which may have a flat surface engagement with the adjacent face of any one of the upper teeth U. The pawl 62 is urged toward an engaging relationship by gravity. The carriage 60 is normally urged in a left hand direction by an expansive coil spring 65 that acts between a fixed abutment 66 depending from the inner surface of the top wall of the housing 30 and a projecting arm 60A that is formed at the right hand end of the carriage 60 so as to project generally toward the rocking unit 34, and this arm 66A functions also in limiting the extent of left hand or conditioning movement of the carriage 60, as will be described.

Take-up pawl 52 and the let-out pawl 62 function in holding the rack R in its set position during the periods when the brakes are released, and of course they function in performing the take-up or let-out operations. A holding pawl 68 is also provided which is ineffective during the brake-off periods, but which is rendered effective and serves as the holding means for the rack R during brake application. The holding pawl 63 is mounted on a pivot pin 69 that extends between the side walls of the housing 30 beneath the rack R, and the pawl 68 com prises one arm of a three-armed unit, and the arm that affords the pawl extends to the left from the pivot pin 69. The pawl 63 has an arm 68W extending to the right and the arm 68W is wide and heavy so as to constitute a weight which tends to rock the pawl 63 in a clockwise direction so as to thereby engage the pawl 68 with the rack teeth L. The pawl 68, however, is held out of engagement with the rack teeth L during the brake-01f periods due to engagement of an upwardly projecting arm 68A of the pawl by the left hand end of the carriage 50. When the carriage 50 is moved to the right, as will be described, in the course of a brake application, the pawl 68 is allowed to engage one of the rack teeth L so that it is the pawl 63 which holds the rack R in position against the brake applying forces.

The carriages 50 and 66 are operated through reciprocating movements in opposite directions in the course of a brake-applying and brake-releasing operation, and such movements are attained by effectually coupling the carriages 5t) and 69 to the rocking unit 34 which has its inner or left hand end, as viewed in FIG. 6, projecting through the adjacent wall of the housing 30. Thus, the rocking unit 34 has a circular head 34H that is rotatably disposed within the complemental opening within the side wall of the housing 30, and means are provided on the left hand end face of this head, FIG. 6, for actuating the carriages 50 and 69.

In the present instance, these connections between the head 34H and the carriages are somewhat in the nature of geared connections. Thus, on the left hand face of the head 34H, a projection is formed in which a plurality of gear teeth 34T are arranged to mesh with complemental gear teeth StlT formed as an upwardly facing rack on and projected laterally from one side of the carriage 50. By engagement of the teeth MT and StiT, the carriage 50 may be reciprocated throughout a limited range along the rack R by rocking movement of the rocking assembly 34, and there is a positive timed relationship of such reciprocating movement and such rocking movement in both directions of operation.

The head 34H also has means thereon for controlling and limiting the movement of the upper carriage 60. Thus, an abutment shoulder 34S facing in a clockwise direction, as viewed in FIGURES 3 and 4A, and having a surface formation quite like one side of the teeth 34T, is arranged to engage an abutment shoulder 60S onthe carriage 6t), and the arrangement is such that when the rocking assembly 34 is rotated in a clockwise direction by the spring 40 to the limit established by engagement of the carriage 56 with the holding pawl 68, the carriages 5t) and 60 will occupy the normal positions shown in FIG. 3. In the actuation of the rocking member 34 in the counterclockwise direction in the course of a brakeapplication, the lower carriage St) is moved to the right, and the upper carriage 60 is allowed to move to the left under the influence of its spring 65. Such left hand movement of the carriage 6% is timed approximately with the movement of the carriage 56, but is terminated by engagement of the arm 69A with an arcuate surface 34A formed on the head 34H. Thus, the carriage 60 comes to rest, while continued rocking movement of the member 34 in a counterclockwise direction will cause continued right hand conditioning stroke of the carriage 50.

In such movements, a cam 56C formed on the carriage 50 is arranged to move under a laterally projecting arm 62A on the let-out pawl 62, and during the brake release operation this attains a controlling action in respect to the let-out pawl 62, as will be described.

When the carriages 5t and 60 are moved in their opposite or return directions toward their home positions, these home positions are determined by engagement of the rear or left hand vertical face of the cam 50C at 50H, FIG. 3, with the opposed right hand face of one of the downward flanges 60F of the carriage 60.

The Normal Shifting Movements of the Rack R Before considering the manner of operation of the con trol unit 20 in the various types of brake applying cycles,

cooperation of the take up pawl 52, and the let out pawl egozsese 6 62 and the holding pawl 63 with the teeth of the raclt'R is dependent in part upon the longitudinal relation of the rack and its teeth to'these pawls.

Thus, when a brake application is initiated, there is an advancing movement of the push rod 25 which starts to take up the slack in the braking system, and when this movement of the push rod has taken up the lost motion between the bracket 25B and the adjusting nuts 27, the cycle of operation of the slack adjusting unit 21 is initi'ated. Up to this point in the brakingcycle, the rack R has been urged in a right hand direction, FIG. 3, but has been held against appreciable movement by the take up pawl 52. However, in the first portion of the right hand 01' conditioning movement of the take-up carriage 5d, the holding pawl 68 is released for movement to its engaged relationship with respect to the rack R, and since the carriage St) is at this time moving toward the right as viewed in FIG. 3, the holding pawl 68 will be engaged by a particular one of the lower teeth L of the rack R, that that thereafter in the braking cycle, the rack Q is held against right hand displacement by the anchoring action of the holding pawl 68. As soon as the holding pawl 68 assumes control of the rack R, the locking engagement of the pawl 52 with the tooth with which it has been engaged is released, and the pawl 52 is free to drop down and out of engagement with respect to rack R, it being noted that at certain other points in the stroke of the carriage 59', the pawl 52 will be urged toward engag ement with the rack by the pawl weight 55 under control of the cam 57.

The rack R is thus anchoredin a fixed position by holding pawl 68 early in the brake application cycle, and as the extension or actuation of the push rod continues; the brake shoes are brought into braking engagement with the car wheels and the push rod movement is terminated.

According to common practice, the push rod stroke should be kept within a limited range which for purposes of explanation will be assumed to be between seven and nine inches, and any stroke greater than nine inches indicates that slack should be taken up in the system, while a push rod stroke of less than seven inches indicates that slack should be let out in the braking system. The need for a take up operation arises because of wear in the system and particularly due to progressive wear of the several brake shoes. The need for let out operation arises when one or more worn brake shoes are removed and replaced by new and relatively thick brake shoes.

In a Long Push Rod Stroke In FIG. 8 of the drawings, 1 have illustrated graphically, and in a somewhat diagrammatic manner, three lengths of push rod strokes, and have indicated the portion of such stroke which constitutes lost motion and what portion constitutes the operating cycle of the control unit 29. FIG. 8 further illustrates the operation of the rack R in the release cycle of such push rod operations, and it might be noted that FIG. 8, in this regard, should be read from right to left. Thus, in FIG, 8, the line 70 indicates a control unit operation where the push rod travel is just under nine inches, or in other words, just long enough to indicate that a take-up operation of the control unit should take place.

In line 71 of FIG. 8, it is indicated that in the release cycle. of the braking apparatus, the rack R starts a return movement and shifts gradually to the left at a rate that is generally proportional to rate of the return stroke of the push rod 25.

This return or left hand movement of the rack R serves in the long cycle, and in the normal cycle, of operation of the unit 20 to move the tooth U-6 into position beneath the pawl 62 before this pawl is released by the cam 50C, and in contrast to this, in a short cycle of operation of the unit 28', the return or left hand movement of the rack R does not progress to the same extent before the pawl 62 is released,- so that in the short cycle, the tooth 8 U-6 is located to the right of the pawl 62 at the time when the pawl is released. Hence, in a short cycle, the pawl 62 may enter the space between the teeth U-5 and U-6 to accomplish the let out operation as will be described in further detail hereinafter. Thus the gradual relaxation or left hand movement of the rack R in the release of the brakes is utilized under the present invention in enabling the unit 24) to distinguish between a normal stroke of the push rod and a short stroke of the push rod.

In Normal Push Rod Travel In FIG. 8 the extent of movement of the push rod in a selected cycle within the normal range is indicated in the line 72 as being eight inches, and the relaxation in the system causes the return movement of the rack R to move the tooth U-6 into position beneath the pawl 22 before the pawl rides oil of the cam 50C.

In Short Push Rod Travel Further comparison is afforded in lines 74 and '75 of FIG. 8 where the push rod movement in a short stroke of just under 7 inches is indicated in line 74, while relaxation or left hand movement of the rack R, as indicated in line 75, does not progress fast enough to locate the tooth- U-6 beneath the pawl 62 prior to release of this pawl.

As will behereinafter described in further detail, the let out pawl 62, at certain times in the cycle of operation of the unit 20, is held in a raised position by the cam 50C of the carriage 5i and in the release cycle, this pawl rides oil of the cam 56C at the same point in the cycle of the control unit 26 as this point is spaced from the normal at rest relation of the parts. This release point for the pawl 62 has been indicated at 76 in FIG. 8, and remains the same regardless of the length of the piston rod stroke. Thus, it may be pointed out generally that the manner of engagement of the pawl 62 with the upper teeth U of the rack R is varied according to the endwise position of the rack R at the same time when the let out pawl 62 rides off of the cam 50C.

In line 71 that pertains to a long stroke of the push rod, and line 73 of FIG. 8 that pertains to the normal stroke of the push rod, it will be evident that by the time the pawl 62 is released the rack R has moved to the left (indicated along the vertical scale) in an amount sufiicient to locate the tooth U-6 under the pawl 62, but in contrast to this, as shown in line 75 of FIG. 8, pertaining to a short push rod stroke, it will be evident that by the time the pawl 62 is released, the rack R has moved a somewhat smaller distance to the left, so that when the let out pawl 62 is released by the cam 50C, the pawl 62 may enter the tooth space between the teeth U5 and U-6. This mechanical distinction is provided between the normal push rod operation and the short push rod operation. This causes the let out pawl 62 to drop into engagement with the rack R during the return or right hand movement of the carriage 60 so as to cause a let out operation of the unit 20, as will be explained hereinafter.

Normal at Rest Relationships of the Parts In FIGS. 3, 4 and 7 the parts of the unit 20 are illustrated in the normal positions which they occupy when the brakes are released, while among the several views that illustrate sequential operations of the unit, FIG; 9 shows the at rest positioning of the parts in a diagrammatic fashion as the several pawls 52, 62 and 68 are related to particular teeth of the rack R. Thus, when the brakes are released, the lower end of the arm 36 of the unit 20' is located and in its most left hand or home position of FIG. 9, and the lower carriage 50 is in engagement with and has withdrawn the holding pawl 68. This home position of the carriage 50 has been diagrammatically indicated by reference to an indicating or index line that is so located as to be aligned with the right hand edge of the carriage 50 when the carriage is in home position. Thus, displacement of the carriage 50 with respect '9 to the index line 150 in FIGS. 9 to 22 is indicative of the extent to which the carriage 50 has been moved from its home position.

Similarly, the upper carriage 66 is at this time in its most right hand or home position shown in FIGS. 3 and 4; and in FIG. 9, the relationship is indicated by location of the center of the pivot pin 63 opposite a fixed indicating or index line 163. Hence, displacement of the carriage 60 in subsequent diagrammatic views is shown by the horizontal distance between the pivot 63 and the index line 163.

When the upper and lower carriages 56 and 6% are thus disposed in their home positions, the pawls 62 and 52 bear a predetermined relation to particular teeth U and L of the rack R, and for illustrative purposes the teeth U and L, as shown in FEGS. 9 to 22, have been numerically identified and differentiated. Thus, in the diagrammatic views, the lower rack teeth have been numbered from left to right as teeth U- to U-9; and as a further aid in visualizing the operation of the unit, upper tooth U-7 which is in a position for cooperation with the pawl 62, lower tooth L-7 which is in position for cooperation with lower pawl 52, and lower tooth L-2 which is in position for cooperation with the holding pawl 68, have been shaded to some extent. e

As shown in FIG. 9, the upper or let-out pawl 62 is fully engaged with the tooth U-7, while the lower or take up pawl 52 is partially engaged with the space between teeth L-7 and L-8, and is being acted upon by the pawl weight 55 so that in the event of a right hand shift of the rack R, the pawl 52 will fully engage the tooth L-7 and will limit such shift of the rack R. Further, the holding pawl 68 which is at this time disengaged, is so related to the rack R that in the next brake application the pawl 66 will engage the tooth L-2, as will be apparent hereinafter.

The rack R is shifted from the position thus described, both in normal operations of the unit 20 and in those cycles where take-up or let-out operations take place, and to illustrate such changes in the rack positioning, cooperating index marks 77 and 77R have been included in H68. 9 to 22 on the housing 30 and the rack R, respectively. These index marks are aligned in FIG. 9 where the rack R is in a selected position of rest, and relative displacement of the marks 77 and 77R in other views serve to illustrate the various changed positions of the rack R.

Operation Within the Normal Range In H68. 9, l0 and 11 the operation of the unit 20 in a normal stroke has been illustrated; FIG. 9 showing the relation of the parts prior to the brake application; FIG. showing the relationship at the end of a brake application where the push rod travel is about eight inches, and H6. 11 showing the parts after completion of the brake release.

During the initial portion of the push rod travel, the lost motion between the bracket 25B and the abutment nuts 27 is taken up, and during this time the arm 36 of the unit remains at rest. As the lost motion is thus being taken up, the take up of slack in the brake system is initiated and will apply right hand forces to the rack R to move the same until the pawl 52 fully enters the tooth space and engages the tooth L-7, whereupon right hand shifting movement of the rack R is temporarily stopped. In the course of initial right hand movement of the rack R the pawl 62 is of course raised so that it rests on top of tooth U-6.

When the lost motion has been taken up, movement of the arm 36 of the unit 20 is started. As the movement of the arm 36 progresses, the lower carriage 50 moves to the right and the upper carriage 60 moves to the left. The cam 50C is moved into position under the pawl 62 so as to exert a controlling action on the pawl 62 during the release operation, as will be described. Inthe right hand movement of the lower carriage 50 and the pawl 52, the rack R also moves to the right, but as this happens the carriage 50 releases the holding pawl 68 in such timed relation that the pawl 68 engages the tooth L-2 so as to stop movement of the rack R in the position in which it is shown in FIG. 10.

The movement of the carriage 60' continues until the upper carriage reaches the limit of its left hand movement as shown in FIG. 10, and after the carriage 60 has stopped, the lower carriage 50 continues its right hand movement in timed relation to the rocking movement of the arm 36. As the lower carriage 56 moves to the right the follower 55F moves into contact with the cam 57 so that the pawl weight 55 is disabled for a portion of the stroke and the pawl 52 drops downwardly. Then the follower 55F passes the cam 57 and the pawl 52 is urged toward the rack R, but since the cycle illustrated in FIG. 10 is a normal cycle of substantially eight inch push rod travel, the pawl 52 engages the end edge of the tooth L8 and does not enter a tooth space. It may be noted that since the pawl 52 has not entered a tooth space, it will be inactive in the return movement of the carriage 51), as will be described.

In the brake release operation, after a normal stroke of the push rod, the parts of the unit 20' return from the position shown in FIG. 10 to the position shown in FIG. 11, and it should be observed that the position shown in FIG. 11 corresponds with the position shown in FIG. 9. In other words, the rack R has been returned to its original position and there has been no take-up or let-out operation of the unit.

In the course of the release operation, it will be observed that the rack R moves to the left from its working position toward its returned position, as indicated along the vertical scale by the sloping line 73A, and this movement is roughly proportioned to the push rod return travel. in the selected example, this return movement progresses to such an extent that the tooth U-6 of the rack R is located beneath the pawl 62 before the pawl 62 rides ofi the cam 50C, it being recalled that this release of pawl 62 takes place at a predetermined point 76 in the operation of the unit 20 regardless of the length of the push rod stroke.

During the time when the rack R is moving to the left as aforesaid, the return movement of the lower carriage 50 is initiated and the follower SSP engages the cam 57 so that the pawl weight 55 is rendered ineffective and the pawl 52 drops out of engagement with respect to the rack R. Similarly, the cam 50C remains in its position beneath the pawl 62 so that the upper or let-out pawl 62 is held in its raised or ineffective position until the point 76 in the cycle has been reached. While the pawl 62 is supported by the cam 50C, the relaxation movement of the rack has progressed somewhat more than one-half one tooth space to the left, and has served to locate the top of the tooth U6 directly beneath the upper pawl 62. Hence, as the return movement of the upper carriage 6t] continues, and the left hand return movement of the lower carriage 50 and its cam 50C continues, the upper pawl 62 is finally released at the point 76 indicated in FIG. 8, and the upper pawl 62 drops into the tooth space adjacent the upper tooth U-7 as shown in FIG. 11. This is the same tooth space that the pawl 62 occupied prior to the operation of the unit.

As to the lower pawl, the cam 57 has retained control of the pawl weight 55 until after the relaxation movement of the rack R has moved the tooth L-7 beyond the pawl 52, and hence, as the carriage 50 continues its left hand return movement, the pawl 52 moves into the tooth space between the teeth L-7 and L8, this being the original space that the pawl occupied prior to the operation of the unit 20.

11 Operation When the Push Rod Stroke Exceeds the Normal Range The operation of the unit 20 when the push rod exceeds the normal range is shown in FIGS. 12 to 14, and in such an operation the unit 20 is effective to cause fake-up operation in which the rack R is shifted one tooth to the left to the position shown in FIG. 14.

The at rest position of the parts is shown in FIG. 12 and is exactly the same as in FIGS. 9 and 11 previously described. In the initial portion of the brake application, the movements of the parts of the unit 12 are exactly like the movements previously described that take place in a normal push rod stroke, and the important distinction re-' sides in the added rocking movement of the arm 36 which results in added conditioning travel of the lower carriage 51? toward the right. The upper carriage 69, however, has a limited conditioning travel so that its conditioning travel in a long stroke of the push rod is the same as in the normal push rod stroke.

7 The added travel of the lower carriage t and its cam 50C will be evident by a comparison of FIG. 13 with FIG. 10, and it will be evident that as a result of this added conditioning travel of the lower carriage 50 toward the right, the lower pawl 52 rides olf of the end of the tooth L-S. In this respect, FIGS; and 13 should be compared. When this occurs, the cam follower 55F has moved to the right beyond the effective range of the stationary cam 57 so that the lower pawl 52 is being urged upwardly, and as a result, the lower pawl 52 enters the tooth space between the teeth L-8 and L-9, as shown in FIG. 13. Thus, at the end of a brake application where the push rod stroke exceeds the normal range, the parts occupy the relationships shown in FIG. 13.

In the brake release operation, the lower carriage 50 immediately starts its return movement to the left, and the face of the lower pawl 52 engages the tooth L8, as shown in FIG. 13, and is thus locked in engagement with this tooth and will maintain such engagement so long as there is an effective endwise force acting between the pawl 52 and the tooth L8. The left hand force is of course applied to the carriage 50 by the return spring 40 of the unit 20 so that so long as the braking system remains under substantial tension, the pawl 52 cannot cause left hand movement of the rack R. However, when the tension on the rack R is reduced to an amount that is less than the force applied by the take-up pawl 52, the rack R is moved to the left by the action of the pawl 52. This left hand movement of the rack R constitutes a take-up operation in the braking system. It might be pointed out that the pawl weight 55 in the release cycle goes through its normal movements as the follower 55P moves under the cam 57, but as above pointed out, the take-up pawl 52 has been locked in its engaged relationship with the rack so that in such release cycle, the operation of the pawl weight 55 may be said to constitute an idle cycle thereof.

In the brake release cycle that takes place, as above described, after a long push rod stroke, it should be observed that while the lower pawl 52 has entered a different tooth space and has effected a take-up operation on the rack R, the upper pawl 62 drops into the same tooth space that it occupied at the beginningof the cycle of operation of the unit 20, and this will be evident by comparison of FIGS. 12 and 14. Furthermore, the position of the parts shown in FIG. 14 is somewhat different than the position shown in FIG. 12, this being caused by the fact that the pawl 52 remains in engagement with the tooth L8 while the upper pawl 62 engages the tooth U-7. This relationship serves to hold the rack R in position against inertia forces that may arise because of coupling and like operations. However, the fact that the lower carriage 50 has not fully returned to its initialposition allows the holding pawlv 68 to remain in an engaged relationship. However, as the rack R has been moved to the left, the holding pawl 68 has moved into 12 the tooth space between the teeth'L 3 and L-4, and while all of the parts of the unit have not assumed full-y restored positions, the rack R has nevertheless been dis placed sufiiciently to the left to cause take-up operation of the system.

In FIGS. 15 and 16, when taken in connection with FIG. 14, the next braking cycle has been illustrated, and because there has been a take-up operation of the sys tem, this next operation of the unit 26 may be classified as a normal operation. Thus in the next braking appli-' cation, the parts of the unit 26 move from the positions shown in FIG. 14 to the positions shown in FIG. 15. The holding pawl 68 becomes effective on the tooth L-3 rather than on the tooth L-2 which it engaged prior to the take-up operation of the unit. Similarly, the upper pawl 62 assumes a position over the upper tooth U-6 rather than over the upper tooth U5.

In the brake release operation, the parts return to the positions shown in FIG. 16 and go through a cycle of movements exactly like the movements described with respect to the FIGS. 10 and 11, with exception, however, that the various pawls cooperate with a different group of teeth of the rack R. Thus, at the end of the brake release cycle, as shown in FIG. 16, the lower pawl 52 is partially engaged with the tooth space between the teeth L'-8 and L- as distinguished from the position of engagement shown inFIG. 12. Furthermore, the upper pawl 62 engages with the tooth space between the teeth U-7 and U-8 rather than between the teeth U-6 and U-7. Thus, the parts of the unit 20 have been returned to rest positions corresponding to the positions of FIG. 12, but with the rack R displaced one tooth to the left, or in other words, one tooth in a take-up direction.

Operation When Piston Travel Is Below Normal Range In FIGS. 17 to 20, the let-out operation of the unit in a short piston rod stroke has been illustrated, and since in such operation the parts do not in every instance assume the exact relationships at the end of the cycle that they had in the beginning of the'cycle, FIGS. 21 and 22 have been employed to illustrate the normal cycle of operation that follows a cycle where the push rod travel is less than normal.

I FIG. 17 shows the positions of the parts of the unit 20 in their at rest positions, and these positions are the same as those shown in FIGS. 9 and 12 that have been previously described. In the brake application, the initial movements of the parts are the same as hereinb'efore' described in respect to the normal cycle and the long cycle, but in a short cycle, the lower carriage 50 has a shorter stroke and comes to rest in the position shown in FIG; 18. The upper carriage 60 and the upper pawl 62, however, have substantially the same length of conditioning stroke in a short cycle of operation as in the normal and long cycles. The differences in the stroke of the lower carriage 50 is clearly evident by comparison of FIGS. 10 and 18, the relationship of the carriage 50 to the index mark being substantially different.

With respect to the upper pawl 62, it will be noted that in a shorter stroke as illustrated in FIG. 18, the pawl 62 comes to rest over the top of the upper tooth U-S which is substantially the same as in the normal stroke of the unit, but the relationship of the upper pawl 62 to the cam 50C is somewhat different because of the shorter conditioning stroke that has been imparted to the lower carriage 50. Here again a comparison of FIGS. 10 and 18 is helpful.

The shorter stroke of the carriage 50 also results in a somewhat different relationship of the lower pawl 52' to the rack R, it being noted that in the short stroke of the unit, the pawl 52 remains partially in position be-' tween the' lower teeth 11-7 and L-8.

In the brake release operation, however, a different functioning of the parts takes place, and FIG. 19 of the drawings shows the position of the parts at substantially the time of the release of the pawl 62 by the cam 50C.

In particular it should be noted in FIG. 19 that the return or left hand movement of the rack R, at the time when thepawl 62 is released, has not progressed to such a point that the tooth U-6 is beneath the pawl, but in contrast, has been relatively slower, so that the tooth space between the teeth U-S and U-6 is beneath the pawl 62. This timing is illustrated in FIG. 8 of the drawings where the return movement of the rack R is shown by the line 75A. The different positioning of the rack R in this instance results from the fact that the release has started at a different point in the cycle of the unit 20, so that prior to the point 76 in the cycle, the rack R has not moved through the same proportion of its return stroke.

Thus, as will be evident in FIG. 19, which illustrates the positions at this time in the cycle, the pawl 62 is allowed to enter the tooth space between the teeth U-S and U-6 and as shown in FIG. 19, the pawl 62 has only partially entered the tooth space, but this entry is sufiicient to stop the left hand or relaxation movement of the rack R. It will be evident by a comparison of the index marks 77 and 77R in FIGS. 18 and 19 that the rack R has moved through a part of its normal relaxation movement, but upon engagement of the pawl 62 with the tooth U6, such relaxation or left hand movement of the rack R has been stopped. At this time in the cycle the lower carriage 50 has just engaged the arm 68A of the holding pawl 68 'so that continued return movement of the carriage 50 will complete the withdrawal of the holding pawl 68 to a point where the pawl cannot interfere with the further let out or right hand movement of the rack R, as will now be described.

The arm 36 of the unit 20 will of course continue its return movement from the position shown in FIG. 19 to the position shown in FIG. 20, and as this takes place the lower carriage t) completes its return movement, and when the follower 55F rides off of the lower point of the cam 57, the pawl 52 will be opposite the lower end of the tooth L7. Hence, as the return left movement of the lower carriage 50 is completed the pawl 52 will partially enter the tooth space between the lower teeth L-6 and L-7, as shown in FIG. 20.

As the upper carriage 60 completes its return or right hand movement, the pawl 62 will move from the position shown in FIG. 19 to the position shown in FIG. 20 to impart a slight right hand or let out movement to the rack R so that the parts come to rest in the position shown in FIG. 20. The let out of the rack R has thus been accomplished in part by limiting or stopping its relaxation movement and in part by the return movement of the pawl 62 after it has engaged the rack.

This let out movement that is thus accomplished in a short cycle of operation of the unit 20 shifts the rack R slightly less than one tooth space to the right, and this.

results, in the assumed example, from the fact that the pawl 62 did not fully enter the tooth space between the upper teeth U-S and U-6. The shifting movements of the rack R, however, does amount to substantially a full tooth space so that an elfective let out operation has been accomplished. This will be evident by a comparison of the position of the rack in FIGS. 17 and 20. The parts, however, do not in such-an instance, assume a fully normal relationship with respect to each other and with the rack, and for this reason FIGS. 21 and 22 have been included as illustrating the next normal cycle of the unit 20.

Thus, in such a succeeding normal cycle of the unit 20, the parts move from the position shown in FIG. 20 to the position shown in FIG; 21. In such movements the parts go through substantially the same movements as hereinbefore described, particularly with respect to the normal cycle illustrated in FIGS. 12 to 14.

However, this normal cycle causes the holding pawl 68 to assume a different relation to the rack R, and this is the result of the let out operation thatjhas been described. Thus, the holding pawl '68 moves into engagement with the lower tooth L-l, this being in contrast to its engagement with the lower tooth L2 in the preceding cycle of operation of the unit. This will be evident upon comparison of FIGS. 18 and 21. The pawls 52 and 62, as shown in FIG. 21, assume positions corresponding with the positions shown in the end of a normal brake operation as illustrated in FIG. 10, but it will be noted that the lower pawl 52 in FIG. 21 is located opposite the lower tooth L7 as contrasted with its location opposite the tooth L-8 in FIG. 10. Similarly, the upper pawl 62 in FIG. 21 is located directly over the upper tooth U-4 rather than over the upper tooth U-S, as shown in FIGS. 10 and 18. Hence, when the brakes are applied in a cycle following a short or let out cycle of the unit 20, the rack R is placed under tension in a position that is displaced one tooth to the right of the position that is occupied in the previous brake applying operation. As a result of this, the push rod 25 goes through a normal stroke, and this is evident by the final location of the arm 36 as shown in FIG. 21. This position corresponds approximately with the position shown in FIG. 10 which of course shows a normal cycle in the unit 20.

When the brakes are released, the parts of the unit 20 return from the positions shown in FIG. 21 to the positions shown in FIG. 22, and this relationship of the parts as shown in FIG. 22, is precisely like the initial relationship shown in FIG. 17 except that the rack R has been displaced one tooth to the right from the position shown in FIG. 17. The apparatus has thus been effective to accomplish the desired let out function.

The short stroke operation of the unit 20 has been described with relation to a stroke just slightly less than the lower limit of the normal working stroke, and such a situation probably represents the most frequently encountered situation where a let out operation is required. There are, however, instances where a let out operation must be performed where the operating stroke of the unit 20 is considerably shorter than the stroke hereinbefore described. Such a situation may arise where more than one new brake shoe is substituted in the braking system of the car, and in such an instance, an extremely short stroke such as a stroke of about 4% inches may result in the unit 20. In the unit 20, as herein illustrated, an automatic let out operation will be instituted in such a short stroke, and in FIG. 8 of the drawings, the relaxation or return movement of the rack R in such an extremely short stroke has been indicated at 75B. In such operation, return or relaxation movement of the rack R progresses even more slowly than in the relaxation cycle indicated at 75A so that when the let out pawl 62 is released by the cam 50C, the tooth space between the teeth U-S and U-6 is located beneath the pawl 62 so that the pawl may enter such space and produce a let out operation in the same manner as was described hereinbefore.

Varying Operating and Installation Conditions In the foregoing description, the unit 20 has been assumed to operate through its various types of cycles in response to specific lengths of push rod travel, but it must be recognized that in actual practice, the operation of the unit varies to some extent according to whether or not the car is standing or is moving at the time of a brake application. Thus the points in the piston rod travel at which the various types of operation of the unit are to take place are established in practice with the understanding that there may be slight but relatively unimportant variations in actual performance due to varying conditions that are encountered.

The present unit is adapted for installation on cars having AAR foundation braking systems, and the provision of the lost motion connection between the pull rod 24 and the push rod 25 enables the unit to be coordinated with the braking system in which it is being incorporated so'as to meet operating standards desired. Adjustment of the nuts 27 on the pull rod serves to determine the length of push rod travel that is to establish the lower limit of the normal range, and such adjustment serves also to establish the upper limit of the normal range of operations, the length of such normal operating range is being established by the tooth spacing in the rack R in combination with the form and extent of the cam 57 and the cam 50C. Specifically, it may be pointed out that in the unit 20, as herein disclosed, the tooth space that is employed is inch, the maximum stroke of the upper carriage 60 is about /2 inch, while the maximum stroke of the lower carriage is on the order of 1 /2 inches. Moreover, the at rest relation and the operating sequence of the holding pawl 68 and the take up pawl 52 may be said to resemble an escapement which acts to assure a limited displacement of the rack R as the brakes are applied so that the return of relaxation movement of the rack in the release cycle may be utilized in providing a mechanical distinction between push rod strokes of different lengths.

Conclusion From the foregoing description it will be apparent that the present invention provides a two-way slack adjuster which embodies reliable clutch structures in the nature of a ratchet and pawl so that these clutch structures are in efiect self cleaning and are extremely rugged in use. It will also be apparent that the present invention provides a two-way slack adjuster in which the normal working forces in the brake application are taken by a holding device in the form of a pawl which is rendered ineiiective while the brakes are released, and in which the adjustable ele ment of the unit is maintained in its adjusted relation against undesired displacement due to impacts by the means which are selectively effective for producing let out or take up operation of the adjustable member.

It will also be apparent that the present invention pro vides a two-way slack adjuster wherein the slack adjusting operations in both directions are performed during the brake releasing portion of the braking cycle so that the forces necessary to accomplish such adjusting operations may be minimized.

Thus, while a preferred embodiment of the invention has been illustrated herein, it is to be understood thatchanges and variations may be made by those skilled in the art without departing from the spirit and scope of the appending claims.

I claim:

1. A slack adjuster for use in a railway braking system having an element constituting a tension member in the brake gear and urged in a let out direction as the brakes are applied and through a relaxation movement in a take up direction as the brakes are released, said adjuster comprising a housing, a rigid toothed member movably mounted in said housing and adapted for connection withsuch an element of a braking system, a holding pawl and a take up pawl engageable with said member to hold the same against let out movement, a let out pawl engageable with the member to hold the same against take up movement, an operator mounted in said housing and adapted for connection to the push rod of the braking system for movement through conditioning and return strokes the length of which varies according to the extent of push rod movement, control means in said housing actuated by said operator as the brakes are applied to engage the takeup pawl and the holding pawl in succession and with an escapement action with the toothed member to permit limited displacement of the member in a let out direction to a working position in which it is stopped by the holding pawl, said control means acting in a long stroke of the operator to render said take up pawl effective on the toothed member to impart take up movement thereto, and further control means on said housing actuated by said operator to disengage the let out pawl as the brakes are applied and effective at a predetermined point in the re turn stroke of the operator to free said let out pawl for engagement with the toothed member in difierent relationships according to'the amount of relaxation movement of the member that has taken place-when the let out pawl is freed.-- I

2. In a railway foundation braking system having a dead lever the anchoring fulcrum-of which is urged and tends to move in a'let out direction as the brakes are applied and which fulcrum is urged and tends to move but take-up direction as the-brakes are released, the combination of a two way automatic slack adjuster comprising a stationarily mounted housing, an elongated rack mounted in said housing for longitudinal shifting movement and connected at one end to said anchoring fulcrum to adjust ably govern theslack in the brake gear according tothe longitudinal relation of the rack to the housing, a hold ing pawl on said housing to engage said rack to resist movement of the rack in a let out direction when the brake gear is placed under tension in a brake application, a rocking assembly mounted ori said housing and connected with the push rod of the brake gear for operation through rocking strokes the length of which is varied according to the extent of push rod travel, yielding means operatively connected with said rocking assembly to impart return movement thereto during return movement of the push rod,- a take-up carriage and a let out carriage mounted for'niove'ment'along said rack, take up and let out pawls' on the respective take-up and let-out carriages yieldingly urged toward engaged relationwith respect tothe rack and each having a self locking engagement with the rack, means operated by said rocking-assembly to normally maintain said carriages in home positions wherein said take up and let out pawls both engage said rack to hold the same against undesired longitudinal displacement, said last mentioned means being operable during brake application to cause conditioning movements of said let out carri'a'ge in a take up direction and said take up carriage in a let out direction, means operated when said take up carri'age is in its home position to disengage said holding pawl, control means including a stationary cam for diseh'g'aging'said take up pawl, soon after the start of a conditionirig movement of the take-up carriage and effective to maintain the pawl disengaged until the take up carriage has moved beyond a normal stroke and then to permit engage'rhnt of the take up pawl with the rack, said control means being ineffective to disengage the take up pawl in a return stroke following such engagement, and a cam on said take up carriage effective shortly after the start the start of the conditioning strokes of said carriages to engage the let out pawl to hold the same disengaged and to re-- lease said let out pawl shortly before the completion of the return movements of said carriages, said release of said let out pawl acting when the rocking assemblyhas moved through a normal stroke or a long stroke to engage said let out pawl with the end of a ratchet tooth and acting when the rocking assembly has moved through a short stroke to engage said let out pawl with a tooth space.

3. In a railway braking system, a rigid toothed member constituting. a tension member in the brake gear and urged in a let out direction as the brakes are applied and through a relaxation movement in a take updirection as the brakes are released, an operator connected to the push rod of the braking system for movement through conditioning and return strokes the length of which varies according to the extent of push r'od movement, a frame, a holding pawl and a take up pawl supported relative to the frame for engagement with the toothed member to control movement thereof in a let out direction, said holding and take up pawls being? actuated and controlled by said operator as the brakes are applied to engage the take-up pawl and the holding pawl with different teeth of the toothed member in succession and with an escapement action to permit limited displacement of the member in a let out direction to a working position in which it is stopped by the holding pawl, additional control means effective in a long stroke of the operator to render said take-up pawl effective on the toothed member to impart take up movement thereto,

and a let out pawl supported relative to the frame and engageable with the toothed member to prevent movement of the toothed member in a take-up direction, said let out panel being actuated and controlled by said operator to maintain the let out pawl out of engagement with toothed member as the brakes are released to permit relaxation movement of the toothed member and said operator being effective at a predetermined point in the return stroke of the operator to free said let out pawl for engagement with the toothed member in difierent relationships according to the extent of the relaxation movement that has taken place when said pawl is freed.

4. In a railway braking system having brake gear operated by a push rod of a brake cylinder and including a force transmitting rigid toothed member that is oppositely shiftable in let out and take up directions for adjusting the slack in the brake gear and which is urged in a let out direction as the brakes are applied and is urged through a relaxation movement in a take up direction as the brakm are released, the combination of a pair of pawls mounted for engagement with said toothed member and operated by said push rod with an escapement action to control and permit limited movement of said member in a let out direction from an initial relaxed posi tion to a working position, means by the push rod and operable upon one of said pawls in a brake release operation in response to an unduly long push rod stroke to render said one pawl efiective to impart take up movement to said member to establish a new relaxed position therefor, a third pawl mounted for engagement with the toothed member and control means for said third pawl operated by said push rod and rendered efiective on said third pawl during a brake release in response to an unduly short push rod stroke engage the third pawl with the toothed member to limit the relaxation movement of the toothed member and impart let out movement thereto so as to let out slack in the brake gear and establish another relaxed position for such member, and said control means being responsive in part to the relative rate of relaxation movement of said member to render said third pawl effective to stop said toothed member in its initial relaxed position when the push rod has operated through a normal stroke.

5. A slack adjuster for use in a railway braking system having an element constituting a tension member in the brake gear and urged in a let out direction as the brakes are applied and through a relaxation movement in a take up direction as the brakes are released, said adjuster comprising a housing, a rigid toothed member movably mounted in said housing and adapted for connection with such an element of a braking system, an operator mounted in said housing and adapted for connection to the push rod of the braking system for movement from a home position through conditioning and return strokes the length of which varies according to the extent of push rod movement, a holding pawl connected to said housing for engagement with the rack to hold the same against let out movement, means governed by said operator to disengage said holding pawl at the end of a return stroke of the operator and engage the holding pawl with the member at the beginning of a conditioning stroke of the operator, a take up pawl and a let out pawl, first and second control means in said housing actuated by said operator to effect engagement of both the take up pawl and the let out pawl with the tooth member when said operator is in its home position and to disengage said let out pawl and said take up pawl after said holding pawl has been engaged, said first control means acting in a long stroke of the operator to render said take up pawl effective on the toothed memher to impart take up movement thereto, and said second control means operating at a predetermined point in the return stroke of the operator to free said let out pawl for engagement with the toothed member in ditterent relationships according to the amount of relaxation movement of the member that has taken place when the let out pawl is freed.

References Cited in the file of this patent UNITED STATES PATENTS 593,553 Nicholson et al Nov. 9, 1897 1,074,558 OBrien Sept. 30, 1913 1,801,854 Farmer Apr. 21, 1931 1,947,405 Camp Feb. 13, 1934 1,991,262 Sauvage Feb. 12, 1935 2,886,145 Vaught et a1 May 12, 1959 

